diff --git a/compiler/optloop.pas b/compiler/optloop.pas
index b6579fa111..a9cfffb2c8 100644
--- a/compiler/optloop.pas
+++ b/compiler/optloop.pas
@@ -275,6 +275,8 @@ unit optloop;
             end;
           typeconvn:
             result:=is_loop_invariant(loop,ttypeconvnode(expr).left);
+          addn,subn:
+            result:=is_loop_invariant(loop,taddnode(expr).left) and is_loop_invariant(loop,taddnode(expr).right);
           else
             ;
         end;